1. Field of the Invention
The present invention relates generally to motorcycle clutches. More particularly, the present invention relates to clutches for off-road racing motorcycle applications.
2. Description of the Related Art
Off-road racing motorcycles intended for older, and often more experienced, riders often utilize a manually controlled clutch and a multiple speed transmission, offering up to five or six different gear ratios. Conversely, most off-road motorcycles for riders of four to nine years in age utilize an automatically engaging clutch and single-speed transmission.
Eliminating the need to shift gears and control the engagement of the clutch reduces learning time for younger, or inexperienced, riders. An automatically engaging clutch also improves safety by allowing inexperienced riders to fully concentrate on maneuvering the motorcycle. Furthermore, in off-road motorcycle competitions (e.g., motocross races), riders in certain age groups and/or engine displacement categories, are required to ride a single speed motorcycle equipped with an automatically engaging clutch.
However, the clutch is not only used by motorcycle riders and racers when shifting the transmission, but is also used to control the overall speed and power delivery of the motorcycle by interrupting engine torque from reaching the rear wheel. For example, the rider may slow the overall speed of the motorcycle while negotiating a comer by briefly disengaging the clutch, instead of altering the throttle position. This method keeps engine speed high in order to have substantial engine torque available immediately upon subsequent re-engagement of the clutch. Experienced off-road motorcycle riders also use a manual clutch to produce a xe2x80x9cburstxe2x80x9d of acceleration, irrespective of shifting the transmission.
A rider of a motorcycle having an automatically engaging clutch must reduce the position of the throttle to slow the speed of the motorcycle in order to negotiate a comer. Upon exiting the comer, as the rider increases the throttle position, there is a delay in engine torque reaching the rear wheel of the motorcycle due to the time that is necessary for the automatic clutch to re-engage. While this condition may be tolerable for recreational or novice riders, it presents a disadvantage to experienced riders, and racers, of motorcycles having an automatic clutch.
Therefore, a need exists for an improved automatically engaging clutch that may be disengaged without having a delay in torque transfer upon subsequent re-engagement.
It is therefore an object of a preferred embodiment to provide a motorcycle clutch utilizing engagement balls capable of radial movement upon ramped surfaces, at engine speeds above a predetermined threshold, in order to automatically engage the clutch and pass engine-produced torque through the clutch to the transmission and, eventually, to the rear wheel of the motorcycle. The clutch additionally includes a release plate is provided for permitting manual disengagement of the clutch while in its automatically engaged mode.
As a related object, ball detents are provided to allow the engine velocity required for engagement of the clutch to be altered by selection of the diameter of ball detents.
According to another object, the angle of the ramped surfaces provided for directing the engagement balls may be changed so as to alter the portion of force distributed axially to engage the clutch.
According to a preferred embodiment, a motorcycle clutch assembly comprises a drive portion, which acts as an input of the clutch and is configured to be driven by an output of a motorcycle engine. A driven portion of the clutch acts as the output of the clutch and is configured to drive a secondary gear of a transmission of a motorcycle. A pressure plate is coupled for rotation with the drive portion and is capable of axial movement from at least a first position to a second position. A release plate is coupled for rotation with the driven portion and is capable of axial movement from at least a first position to a second position. A plurality of drive clutch plates coupled for rotation with the drive portion and a plurality of driven clutch plates coupled for rotation with the driven portion are arranged, in an alternating manner, between the pressure plate and the release plate. The clutch has at least a first mode wherein the pressure plate is in its second position and no engine torque is transferable from the drive portion to the driven portion. The clutch has at least a second mode wherein the pressure plate is in its first position, the release plate is in its first position and engine torque is transferable from the drive portion to the driven portion. The clutch additionally has at least a third mode wherein the pressure plate is in its first position and the release plate is in its second position wherein no engine torque is transferable from the drive portion to the driven portion.
A clutch configured in this manner provides at least three advantageous modes of operation. In the first mode, the pressure plate is not exerting pressure on the plurality of clutch plates and relative rotation is allowed between the drive clutch plates and driven clutch plates. Therefore, no torque is transferred between the engine and transmission. In a second mode, the pressure plate has moved to its first position and the drive clutch plates and driven clutch plates are coupled between the pressure plate and release plate. In this mode, engine torque is passed through the clutch assembly to the transmission, and eventually the rear wheel of the motorcycle. In a third mode, the pressure plate is, again, in its first position, however, the release plate is axially displaced away from the assembly of clutch plates, to its second position, once again permitting relative rotation between the drive and driven clutch plates. In this mode, no torque is passed through the clutch assembly. Thus, no engine-produced torque reaches the transmission and, subsequently, the rear wheel of the motorcycle.
Advantageously, a clutch configured substantially as described above is capable of automatic engagement at engine speeds above a predetermined threshold. In addition, the clutch may be manually disengaged and subsequently re-engaged without a delay in torque transfer.
According to a preferred embodiment, a motorcycle comprises a frame and an engine, having an output shaft, is connected to the frame. A transmission, having a transmission input shaft, is fixed relative to the engine. A clutch is provided, including a drive portion coupled for rotation with the engine output shaft. A driven portion is coupled for rotation with the transmission input shaft. The clutch has a first mode wherein the drive portion and the driven portion are not coupled when the engine is below a predetermined engine speed. The clutch also has a second mode wherein the drive portion and the driven portion are coupled when the engine is above the predetermined engine speed. The clutch has a third mode wherein the drive portion and the driven portion are not coupled when the engine is above the predetermined engine speed.